The solar system

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Planet Earth is part of a vast space neigh­bor­hood called the solar sys­tem. Our solar sys­tem is an amaz­ing place. Our solar sys­tem is one of many groups of plan­ets that are part of the Milky way galaxy. About 15–20 bil­lion years ago, there was an enor­mous explo­sion called the Big Bang. Whirling clouds of dust and gas filled the Uni­verse. Over time, grav­ity made some clouds start to group together. Big groups formed galax­ies. Smaller groups became stars. Then, about 4.5 bil­lion years ago, the clouds that formed our solar sys­tem spun so fast they formed a disk. The cen­ter of the disk became so hot it dropped out. That cen­ter became the sun. The dust and gas that didn’t get sucked into the cen­ter stuck together in groups. These groups became plan­ets. Our solar sys­tem was born. The eight plan­ets of our solar sys­tem revolve around a large star called the sun. The sun is the cen­ter because it’s HUGE. More than one mil­lion Earths could fit inside it. It con­tains more than 99.8% of all the mass in the solar sys­tem. Its size gives it the grav­ity it needs to hold the solar sys­tem together. The sun’s grav­ity pulls the objects down while they keep try­ing to move away. It’s a never-ending tug-of-war that keeps the plan­ets in their orbits instead of fly­ing off into space. Pluto was once the ninth planet in our solar sys­tem. But in 2006, sci­en­tists kicked it out of the lineup. Why? They had come up with new rules about what makes a “real” planet. Pluto just didn’t mea­sure up. Pluto is shaped kind of like a potato. It has a weird orbit that some­times crosses into Neptune’s. And it has a lot of debris orbit­ing around it.